1. Field of the Invention
The present invention relates to an exhaust gas recirculation (hereinafter referred to as EGR) control of an internal combustion engine, particularly to an EGR control technique of a diesel engine. Further the present invention relates to a control apparatus for controlling a volume for injecting fuel oil and an EGR amount in an internal combustion engine. Still further the present invention relates to a technique of estimating pressures in intake and discharge systems which are required for controlling the EGR of the internal combustion engine.
2. Description of the Related Art
Conventional EGR control methods of the internal combustion engine include, for example, a technique disclosed in Japanese Patent Application Laid-Open No.63-129157. The disclosed technique relates to a technique for adjusting EGR in accordance with errors in injection timings.
However, in the above described conventional EGR control method, a rate in which the EGR is adjusted is constant in every operation conditions. Since sensibility of the discharge air is actually different with respect to a load, a gain for adjusting is required to be changed in accordance with the load. However, the prior art can not satisfy this condition so that the EGR is too little in an operation condition or too much in another operation condition. Accordingly, it is difficult to obtain the best discharge of air.
Further, the conventional control apparatuses of the internal combustion engine include Japanese Patent Application Laid-Open No.57-86535 in which the maximum volume for injecting fuel oil (upper limit value of the volume for injecting fuel oil regularly calculated) is adjusted to be reduced under the operation of EGR. Japanese Patent Application Laid-Open No.63-143343 show another control apparatus in which the EGR is stopped together with adjusting to reduce the maximum volume for injecting fuel oil at a time of accelerating operation. These apparatuses are made in view of generation of smoke (PM) in the case that volume for injecting fuel oil is rapidly increased under much EGR amount. In these techniques, a standard value of the maximum volume for injecting fuel oil is set in accordance with the revolution speed of the engine and the like.
However, even if the maximum volume for injecting fuel oil is adjusted to be reduced in the above manner, in the case that the adjustment of the EGR is constantly operated due to the fact whether or not the EGR exists, the maximum volume for injecting fuel oil is not changed in spite of change of the EGR rate so that sufficient output can not be obtained because of insufficient throttling of injection quantity or the smoke is generated because of excessive throttling. Accordingly, it is difficult to obtain both of a good exhausting performance and a good driving performance.
Further, it is understood that when the amount for adjustment with respect to the maximum volume for injecting fuel oil is changed in accordance with a target EGR rate, since there is an air dynamics at a transient, the similar matter to the above mentioned matter occurs.
Still further, in conventional detecting methods of detecting pressures in intake and exhaust systems of the internal combustion engine, it is popular to provide a sensor for directly detecting the pressures. Further, there is a technique disclosed in Japanese Patent Application Laid-Open No.8-284735, in which the pressure is estimated by an output from an air flow meter and the like.
However, in the case that the sensor is provided in the above manner, high cost is required, and in the case of a sensor for detecting the exhaust pressure, since the exhaust gas is recirculated such as the EGR and the sensor is exposed to an high temperature atmosphere, it is very severe in durability. In the case of securing the durability, time constant of the sensor is extremely large and an accurate value can not be displayed in the transient so that it is difficult to feedback to the control.
Further, since the exhaust temperature affecting to the exhaust pressure is changed by parameters such as an injection timing and/or an air flow within an cylinder, the above described technique disclosed in Japanese Patent Application Laid-Open No.8-284735 can not achieve this problem.